This invention relates to a method for cleaning the disassembled components of vacuum deposition equipment of deposited materials and, more particularly, is directed to an efficacious method for the removal of sputtered titanium materials from ultra high vacuum equipment used in semiconductor manufacturing.
It is well recognized that both equipment and material cleanliness are necessary conditions in order to avoid low production yields in the manufacture of integrated circuits. For example, an entire microelectronics circuit is ruined by a single defect. A defect caused by a contaminant particle introduced at any of a number of points in the process will either create a defective product that is immediately recognizable as such, or result in the production of a circuit that fails shortly after being placed into use.
Conditions for cleanliness are established early on in the manufacturing process beginning with the preparation of the semiconductor wafer upon which a multiplicity of processing steps are performed. The variety of steps include diffusion, sputtering and evaporation techniques. During the time that the fabrication of the circuits in the wafers is taking place, extreme care is taken to ensure that the operating environment is clean. To that end, considerable attention is paid to the maintenance of clean equipment. Not only are safeguards taken to prevent the introduction of external impurities, but the equipment is also periodically disassembled into its component parts in order to remove previously deposited process materials. The presence of process material build-up in the vacuum chambers can result in the uncontrolled presence of these materials on the microelectronic circuits and can be as ruinous to the circuit as external containments.
Consequently, the processing equipment is routinely taken apart according to schedule, typically a use cycle of approximately one thousand wafer depositions, and subjected to a variety of treatments which attempt to restore the equipment to initial condition. In the case of sputtering equipment wherein titanium and titanium compounds are pattern deposited on the surface of the circuitry being fabricated, the sputter particles migrate throughout the entire chamber and end up being deposited on all exposed surfaces. The failure to thoroughly clean the equipment components within the chamber on a periodic basis is likely to result in the spalling and flaking of deposited material. The result of unpredictable movement of deposited materials in the chamber on to the exposed wafer surface is a reduction in the manufacturing yield caused by an increase in the number of defects in the circuitry produced.
One method of cleaning the components presently used in the fabrication process utilizes a stripping bath containing approximately equal parts of nitric acid, hydrofluoric acid and deionized water. The hydrofluoric acid provides a cleaning and etching effect to the surfaces of the components while the nitric acid promotes the solubility of deposited metal and metal compounds. The two acids provide complimentary action and act more rapidly at an elevated bath temperature. Considerable care must be taken to ensure that the welds of the treated structural components are not weakened by the effects of the hydrofluoric acid. Thus, a balance is attempted to be maintained between reducing the hydrofluoric acid ratio and the temperature of the bath. The reducing of the bath temperature produces a corresponding reduction in the activity of the acid bath thereby requiring a longer immersion time to achieve the same stripping effect.
Following the stripping of deposited materials, the components are normally subjected to a power wash which removes macro and micro particles that tend to remain on the surface of the components. The wash typically uses deionized water and precedes a drying step. The drying occurs in an oven provided with an inert gas environment. At the completion of the drying, the components are reassembled in the sputtering chamber and the manufacturing process is resumed.
In practice, the above-described cleaning process is frequently found insufficient to permit the component to be reinstalled without being subjected again to the process. As mentioned, the foregoing process has the capability of shortening the usable life time of the components since a strong hydrofluoric acid bath tends to weaken the structural integrity of the component.
Accordingly, the present invention is directed to a controllable method of cleaning components of semiconductor fabrication equipment which utilizes a low temperature bath for stripping of deposited materials. In addition, the subject method utilizes a stripping bath that does not include hydrofluoric acid. Another objective of the invention is the provision of a method of cleaning which prepares the surface of the treated components to receive deposited material in an adhering manner when the equipment is again placed in use.